118 A MANUAL OF THE PENICILLIA 



and effort. Even then, exact duplication of morphology or biochemical 

 activity is usually not achieved. 



New Species 



Individual strains, or groups of strains, are occasionally encountered 

 which differ from all recognized forms sufficiently to warrant the description 

 of new species. Usually such forms can be diagnosed as belonging to one 

 or another of the general series which constitute the genus. Careful con- 

 sideration and detailed comparison of related species in culture, together 

 with extensive review of the published literature, must precede any thought 

 of species description. The Avorker should realize that many species of 

 Penicillium have already been described by many mj^cologists in many 

 different laboratories working over a period of many years. Of course this 

 does not mean that new material warranting description will not be en- 

 countered, particular^ when special types of natural substrata are in- 

 tensively examined, or when out-of-the-ordinary techniques of isolation 

 are employed. It does mean, however, that one should have a full appre- 

 ciation of earlier taxonomic studies in the genus, and that one should 

 exercise the greatest possible care to avoid replication of such studies. 



Recognized Species 



Of more than seven hundred species of Penicillium that have been de- 

 scribed, a total of 137 are recognized in this Manual. The authors realize 

 that mistakes have undoubtedly been made. In some cases valid species 

 may have been reduced to synonymy through our lack of understanding 

 of the true characteristics of the species as originally described. In other 

 cases we may have selected for continued recognition species which were 

 originally too vague and indefinite to warrant species status. Throughout 

 the study we were motivated by the firm conviction that much duplication 

 in description had undoubtedly taken place in different laboratories where 

 comparable source materials were not studied. Furthermore, we were 

 convinced that no mycologist could hope to distinguish between all of the 

 forms that have been described. In large measure, the development of a 

 satisfactory and useful taxonomy of the genus Penicillium seemed to hinge 

 upon two premises: First, that the number of species of Penicillium was 

 too large and must be reduced; and second, that the species selected for 

 continued recognition should be presented in as tangible, specific, and re- 

 producible terms as possible. 



Throughout our study we have endeavored to recognize those species 

 which, by priority or common usage, have come to be most generally . 

 accepted. Furthermore, we have endeavored to center the description and 

 discussion of recognized species around the tj^pe strains of such species un- 



